Heterogeneous amorphous phases

FIGURE 11.19 Arrhenius diagram of a heterogeneous amorphous phase. 

In order to anticipate problems and to interpret observations under the extreme conditions of shock compression, it is necessary to consider structural and electronic characteristics of PVDF. Although the phenomenological piezoelectric properties of PVDF are similar to those of the piezoelectric crystals, the structure of the materials is far more complex due to its ferroelectric nature and a heterogeneous mixture of crystalline and amorphous phases which are strongly dependent on mechanical and electrical history. 

Clarity is noted when the light passes through a homogeneous sample, such as a crystalline, ordered polymer or a completely pure amorphous phase. Interference occurs when the light beam passes through a heterogeneous... 

The forms of active components present in heterogeneous catalysts are of importance to catalysis. A supported catalyst usually consists of an active component dispersed on a support with a highly specific surface. According to current opinions (/), an active component dispersed on a support may end up in one of three forms (1) it may retain its chemical identity as a separate crystalline or amorphous phase, (2) it may form a new stoichiometric compound with the support or additive, or (3) it may dissolve in the support to give a solid solution. Examples of these forms are readily available from the literature. 

Historically, polysiloxane elastomers have been reinforced with micron scale particles such as amorphous inorganic silica to form polysiloxane microcomposites. However, with the continued growth of new fields such as soft nanolithography, flexible polymer electronics and biomedical implant technology, there is an ever increasing demand for polysiloxane materials with better defined, improved and novel physical, chemical and mechanical properties. In line with these trends, researchers have turned towards the development of polysiloxane nanocomposites systems which incorporate a heterogeneous second phase on the nanometer scale. Over the last decade, there has been much interest in polymeric nanocomposite materials and the reader is directed towards the reviews by Alexandre and Dubois (4) or Joshi and Bhupendra (5) on the subject. 

The peak width of the a-relaxation process is a probe for the heterogeneity of the chain environment in the amorphous phase of the sample. For material C a variation of the peak width was found if the extrusion conditions had been changed. This effect was attributed to the changing number of tie molecules under different extrusion conditions. 

The whole simulations are performed according to the following procedure. First, elastic constants of PTT in amorphous phase Camor are calculated using the atomistic modeling, which will be used as input values for the matrix CP in the atomistic-continuum model. Second, elastic constants of PTT in crystalline phase CCTSt are also evaluated in the same manner as those of amorphous PTT. Third, the atomistic-continuum model is validated for heterogeneous material by comparing the calculated elastic constant for the system of infinite lamellas with its exact solution. Finally, elastic constants of semicrystalline PTT with dif-... 

The remainder of this chapter will focus on the thermal conductivities of amorphous polymers (or the amorphous phase, in the case of semicrystalline polymers). See Chapter 20 for a discussion of methods for the prediction of the thermal conductivities of heterogeneous materials (such as blends and composites) in the much broader context of the prediction of both the thermoelastic and the transport properties of such materials. 

It has therefore been concluded that (i) the most common process of zeolite nucleation relies on a primary nucleation mechanism and (ii) the most probable primary nucleation mode is heterogeneous and centred upon the amorphous phase of the reaction mixture (which for most clear solution syntheses is colloidal in nature). 

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